Light emitting element having an organic layer including a light-emitting layer

ABSTRACT

This present invention provides a light emitting element comprising at least one organic layer containing a light emitting layer provided between a pair of electrodes, and in this structure, at least one layer of the at least one organic layer contains at least one compound consisting essentially of carbon, fluorine and nitrogen.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 10/644,830 filed Aug. 21,2003, now U.S. Pat. No. 7,189,989 which claims priority under 35 USC 119from Japanese Patent Application No. 2002-241663. The entire disclosuresof application Ser. No. 10/644,830 and Japanese Patent Application No.2002-241663 are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting element such as a anorganic electroluminescent element. Particularly, the present inventionrelates to a light emitting element that has high luminance and luminousefficiency, and also has superior endurance.

2. Description of the Related Art

In recent years, organic electroluminescent (EL) elements have beenactively investigated and developed, since these elements can emit lightwith high luminance through a low-voltage driving process. In general,an organic EL element is constituted by a light emitting layer and apair of opposing electrodes that sandwich this layer, and electrons,injected through a cathode, and holes, injected through an anode, arerecombined in the light emitting layer so that excitons are generated,and utilized to emit light.

Recently, organic EL elements have become highly efficient. The externalquantum efficiency of an organic EL element using an iridium complex asa light emitting material has exceeded 5%, which had been conventionallyconsidered as a limit, and reached 8% (Applied Physics Letters, Vol. 75,page 4, published in 1999).

Japanese Patent Application Laid-Open (JP-A) No. 2001-247498 disclosesan organic EL element using a material consisting of carbon andfluorine.

However, the conventional organic EL elements fail to provide sufficientendurance, and there is strong demand for development of organic ELelements having high luminance, high luminous efficiency, and superiorendurance.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide an organic EL elementthat has high luminance, high luminous efficiency, superior color purity(in particular, purity of blue), and superior endurance.

The present invention provides a light emitting element comprising atleast The present invention provides a light emitting element comprisingat least one organic layer which includes a light emitting layer, andwhich is disposed between a pair of electrodes, wherein at least onelayer of the at least one organic layer contains at least one compoundconsisting essentially of carbon, fluorine and nitrogen. The compoundscontains hydrogen atoms in an amount of not greater than two hydrogenatoms per six carbon atoms.

In the present invention, the compound consisting essentially of carbon,fluorine and nitrogen is preferably a compound represented by thefollowing general formula (A):X—(R)n   General formula (A)wherein in general formula (A), X represents an aromatic ring group or ahetero cyclic ring group, which have atoms selected from the groupconsisting of carbon, fluorine and nitrogen; R represents a groupconsisting of carbon and fluorine, or a group consisting of carbon,fluorine and nitrogen; n represents an integer of 1 or more; and when Xcontains no nitrogen, at least one R contains at least one nitrogen.

In the present invention, the compound consisting essentially of carbon,fluorine and nitrogen is preferably a compound represented by thefollowing general formula (I):

wherein in general formula (I), each of Ar¹, Ar² and Ar³ represents anaryl group consisting of carbon and fluorine.

DETAIL DESCRIPTION OF THE INVENTION

A light emitting element of the present invention will be described indetail below.

The light emitting element comprising at least one organic layer whichincludes a light emitting layer, and which is disposed between a pair ofelectrodes, wherein at least one layer of the at least one organic layercontains at least one compound (hereinafter, referred to as “specificcompound”) consisting essentially of carbon, fluorine and nitrogen.

With regard to the above-mentioned specific compound, the expression,“consisting essentially of carbon, fluorine and nitrogen” refers to thefact that most preferably, the compound contains no atoms other thancarbon, fluorine and nitrogen atoms, that is, no atoms, includinghydrogen atoms, other than these atoms. However, with respect tohydrogen atoms, the compound may contain not more than two hydrogenatoms (more preferably, not more than one) per six carbon atomscontained in the compound, and even in this case, the compound makes itpossible to sufficiently provide the effects of the invention.

In the above-mentioned specific compound, the ratio of the number offluorine atoms to the number of carbon atoms contained in a molecule ispreferably from 55% to 90%, more preferably from 57% to 88%, and stillmore preferably from 60% to 85%.

When durability of the light emitting element is taken intoconsideration, a glass transition temperature (Tg) of the specificcompound is preferably from 130° C. to 400° C., more preferably, from135° C. to 400° C., still more preferably, from 140° C. to 400° C.,particularly preferably, from 150° C. to 400° C., and most preferably,from 160° C. to 400° C.

In this case, the glass transition temperature (Tg) can be confirmed bythermal measurements, such as differential scanning calorimetry (DSC)and differential thermal analysis (DTA), X-ray diffraction (XRD),observation under a polarizing microscope or the like.

As will be described below, the light emitting element of the inventionmay utilize either light emission from an excited singlet state or lightemission from an excited triplet state. However, when the light emittingelement utilizes light emission from the excited triplet state, theabove-mentioned specific compound preferably has a minimum excitedtriplet energy level (T₁ level) from 65 kcal/mol (272.35 kJ/mol) to 95kcal/mol (398.05 kJ/mol), more preferably, from 67 kcal/mol (280.73kJ/mol) to 95 kcal/mol (398.05 kJ/mol), still more preferably, from 69kcal/mol (289.11 kJ/mol) to 95 kcal/mol (398.05 kJ/mol), andparticularly preferably, from 71 kcal/mol (297.49 kJ/mol) to 95 kcal/mol(398.05 kJ/mol).

The compound (specific compound) consisting essentially of carbon,fluorine and nitrogen used in the present invention will be describedbelow.

<Compound Represented by General Formula (A)>

Preferable examples of the above-mentioned specific compound used in thepresent invention include a compound represented by the followinggeneral formula (A):X—(R)n   General formula (A)wherein in general formula (A), X represents an aromatic ring group or ahetero cyclic ring group, which have atoms selected from the groupconsisting of carbon, fluorine and nitrogen; R represents a groupconsisting of carbon and fluorine, or a group consisting of carbon,fluorine and nitrogen; n represents an integer of 1 or more; and when Xcontains no nitrogen, at least one R contains at least one nitrogen.

Compounds represented by general formula (A) will be described below.

The aromatic ring group or a hetero cyclic ring group, representing byX, have atoms selected from the group consisting of carbon, fluorine andnitrogen, and X may be a single ring or a condensed ring. Specificexamples thereof include a triazine ring, a pyridine ring, a pyrimidinering, a pyridazine ring, a pyrazine ring, a tetrazine ring, a quinolinering, a quinoxaline ring, an acridine ring, a phenanthroline ring, atetraazaanthracene ring, a hexaazatriphenylene ring, a pyrrole ring, anindole ring, a benzene ring, a naphthalene ring, an anthracene ring, atetracene ring, a phenanthrene ring, a triphenylene ring, a fluoranthenering, a pyrene ring and a perylene ring; among which nitrogen-containinghetero rings are preferable; a triazine ring, a pyridine ring, apyrimidine ring and a pyrazine ring are more preferable, a triazine ringand a pyrazine ring are still more preferable; and the triazine ring isparticularly preferable.

In X, all the carbon atoms which are not substituted with R aresubstantially substituted by fluorine atoms. The groups consisting ofcarbon and fluorine or consisting of carbon, fluorine and nitrogen,which are represented with R, may be the same as or different from eachother. In the case when X contains no nitrogen at least one R containsat least one nitrogen.

With respect to the group represented by R, examples thereof include analkyl group in which all the hydrogen atoms are substantiallysubstituted with fluorine atoms (having preferably, carbon atoms of 1 to20, more preferably, carbon atoms of 1 to 10, and most preferably,carbon atoms of 1 to 6, and examples thereof include a trifluoromethylgroup, a pentafluoroethyl group and a tridecafluorohexane); an arylgroup in which all the hydrogen atoms are substantially substituted withfluorine atoms (having preferably, carbon atoms of 6 to 45, morepreferably, carbon atoms of 6 to 35, and most preferably, carbon atomsof 1 to 25, and examples thereof include a perfluorophenyl group, aperfluorobiphenyl group, a perfluoronaphthyl group, aperfluoroanthracenyl group, a perfluorophenanthryl group, aperfluoroperylenyl group); and a heterocyclic group in which all thehydrogen atoms are substantially substituted with fluorine atoms (havingpreferably, carbon atoms of 4 to 40, more preferably, carbon atoms of 4to 35, and most preferably, carbon atoms of 3 to 25, and examplesthereof include a perfluoropyridinyl group, a perfluoroquinolyl group, aperfluoroacridinyl group and a perfluorothienyl group), among which anaryl group in which all the hydrogen atoms are substantially substitutedwith fluorine atoms is most preferable.

Here, n represents an integer of 1 or more, preferably 2 or more, andmore preferably 3 or more.

The compounds represented by general formula (A) are more preferablythose compounds represented by general formula (I) described below.

<Compound Represented by General Formula (I)>

Preferable examples of the above-mentioned specific compound used in thepresent invention include a compound represented by the followinggeneral formula (I):

wherein in general formula (I), each of Ar¹, Ar² and Ar³ represents anaryl group consisting of carbon and fluorine.

Compounds represented by general formula (I) will be described below.

Compounds represented by general formula (I) will be described below.

In general formula (I), the aryl groups represented by Ar¹, Ar² and Ar³,which consist of carbon and fluorine, may be the same as or differentfrom each other, and may be a single ring or a condensed ring in whichtwo or more rings are condensed.

In general formula (I), each of the above-mentioned Ar¹, Ar² and Ar³, ispreferably a perfluorophenyl group, a perfluorobiphenyl group, aperfluoronaphthyl group, a perfluoroanthracenyl group, aperfluorophenanthryl group, a perfluoropyrenyl group, aperfluoronaphthacenyl group, a perfluoroperylenyl group or the like,among which a perfluorophenyl group, a perfluorobiphenyl group and aperfluoronaphthyl group are particularly preferable.

Moreover, each of the above-mentioned Ar¹, Ar² and Ar³, may besubstituted at an arbitrary position by an aryl group consisting ofcarbon and fluorine. As the aryl group consisting of carbon and fluorineto be used as a substituent, the same groups as described as groupsrepresented by Ar¹, Ar² and Ar³, may be applied, and the preferablerange thereof is the same as that of those groups.

Specific examples of the specific compound of the invention (exemplifiedcompounds(A-1) to (A-6) and (I-1) to (I-10)) are shown below. However,the present invention is not intended to be limited to these examples.

The specific compound represented by general formulae (A) and (I) may besynthesized by various known synthesizing methods. For example, it maybe synthesized by allowing a mono-metalated perfluoroaryl derivative(for example, pentafluorophenyl lithium) to react with cyanuricchloride.

The light emitting element of the present invention may utilize eitherlight emission from an excited singlet state or light emission from anexcited triplet state. With respect to the light emitting element of theinvention, it is preferable to use light emission from an excitedtriplet state. Here, in the present specification, light emission froman excitation singlet state is defined as fluorescent light, and lightemission from the excitation triplet state is defined as phosphorescentlight.

Although not particularly limited, when the light emitting element ofthe invention utilizes light emission from the excited triplet state,examples of the material emitting phosphorescence (hereinafter, referredto as “phosphorescence emitting material”) preferably include transitionmetal complexes, more preferably include complexes such as an iridiumcomplex, a platinum complex, a rhenium complex and a ruthenium complex,and still more preferably include complexes such as an iridium complexand a platinum complex. An iridium complex is particularly preferable.Moreover, among the above-mentioned transition metal complexes, anorthometalated complexes are particularly preferable. The orthometalatedcomplex referred to herein is a generic designation of the group ofcompounds described in Akio Yamamoto, Yûki Kinzoku Kagaku, Kiso to Ôyô(“Organic Metal Chemistry, Fundamentals and Applications”, Shôkabô,1982), pp. 150 and 232, and in H. Yersin, Photochemistry andPhotophysics of Coordination Compounds (New York: Springer-Verlag,1987), pp. 71-77 and pp. 135-146.

A phosphorescence quantum yield of the above-mentioned phosphorescenceemitting material at 20° C. is preferably not less than 70%, morepreferably not less than 80%, and still more preferably not less than85%. In this case, the maximum value of the phosphorescence quantumyield is 100%, and the phosphorescence quantum yield is most preferably100%. Moreover, a phosphor maximum wavelength is preferably from 300 nmto 500 nm, more preferably from 305 nm to 495 nm, further preferablyfrom 310 nm to 490 nm, most preferably from 315 nm to 480 nm.

With respect to a light emitting element system of the light emittingelement of the invention, an organic EL element is preferably used. Inthe organic EL element, the above-mentioned specific compound ispreferably used as an electron transporting material (including a holeobstructing material) or as a host material to be used in a layercontaining the light emitting material, and is most preferably used asthe electron transporting material.

Constituent elements of the light emitting element of the invention willbe described in more detail.

As described above, the light emitting element of the invention has atleast one organic layer which is include a light emitting layer, andwhich is disposed between a pair of electrodes (anode and cathode), andat least one layer of the at least one organic layer contains theabove-mentioned specific compound.

In a case where the specific compound (including the compoundsrepresented by the general formulae (A) and/or (I)) is used as theelectron transporting material, a mass ratio of the compound in the atleast one organic layer containing the compound is preferably from 60 to100% by mass, and more preferably from 70 to 100% by mass. In case ofthe specific compound is used as the host material, the mass ratio ofthe compound in the at least one organic layer containing the compoundis preferably from 50 to 99.9% by mass, and more preferably from 60 to99% by mass.

A method for forming the at least one organic layer in the lightemitting element of the invention is not particularly limited, andvarious methods, such as a resistance heating vapor deposition method,an electrophotographic method, an electron beam method, a sputteringmethod, a molecular accumulation method, a coating method (such as aspray coating method, a dip coating method, an impregnation method, aroll coating method, a gravure coating method, a reverse coating method,a roll brush method, an air-knife coating method, a curtain coatingmethod, a spin coating method, a flow coating method, a bar coatingmethod, a micro gravure coating method, an air doctor coating method, ablade coating method, a squeeze coating method, a transfer roll coatingmethod, a kiss coating method, a cast coating method, an extrusioncoating method, a wire bar coating method and a screen coating method),an ink-jet method, a printing method and a transfer method arepreferred. Among these, from the standpoint of characteristics of theelement, ease of production and cost performance, the resistance heatingvapor deposition method, the coating method and the transfer method arepreferably used.

When the light emitting element has a multilayer structure comprisingtwo or more layers, it is possible to manufacture the layers bycombining the above-mentioned methods.

When a coating method is used as the forming method of the at least oneorganic layer, upon preparing a coating solution, materials and resincomponents to be contained in the respective layers may be commonlydissolved or dispersed therein. Examples of the resin components to beused at this time include: poly(vinyl chloride), polycarbonate,polystyrene, polymethylmethacrylate, polyester, polysulfone,polyphenylene oxide, polybutadiene, poly(N-vinyl carbazole), hydrogencarbide resin, ketone resin, phenoxy resin, polyamide, ethyl cellulose,vinyl acetate, ABS resin, polyurethane, melamine resin, unsaturatedpolyester resin, alkyd resin, epoxy resin and silicon resin.

Additionally, the light emitting element of the invention can exertsuperior light emitting characteristics even when the light emittinglayer is formed by using a coating method which normally fails toprovide high luminous efficiency.

The at least one organic layer in the light emitting element of theinvention contains at least one light emitting layer, and in additionthereto, may contain a hole injecting layer, a hole transporting layer,an electron injecting layer, an electron transporting layer, aprotective layer or the like. Moreover, these layers may respectivelyhave other functions. The specific compound may be contained in any ofthese layers. The respective layers will be described in detail below.

A material for the hole injecting layer and the hole transporting layermay be a material having one of a function of injecting holes from theanode, a function of transporting the holes, and a function ofobstructing electrons injected from the cathode. Specific examplesthereof include a a carbazole, a triazole, an oxazole, an oxadiazole, animidazole, a polyarylalkane, a pyrazoline, a pyrazolone, aphenylenediamine, an arylamine, an amino-substituted chalcone, astyrylanthracene, a fluorenone, a hydrazone, a stilbene, a silazane, anaromatic tertiary amine compound, a styrylamine compound, an aromaticdimethylidyne series compound, a porphyrin series compound, a polysilaneseries compound, a poly(N-vinylcarbazole), an aniline series copolymer,and an oligomer of an electroconductive polymer, such as a thiopheneoligomer and polythiophene, or derivatives of these compounds.

Film thickness of the hole injecting layer and the hole transportinglayer are not particularly limited, and in general, are preferably from1 nm to 5 μm, more preferably from 5 nm to 1 μm, and still morepreferably from 10 nm to 500 nm.

The hole transporting layer may have a single layer structure of one ormore kinds of the above-mentioned materials or, alternatively, amultilayer structure comprising plural layers having the samecomposition or different compositions.

A material for the electron injecting layer and the electrontransporting layer may be a material having one of a function ofinjecting electrons from the cathode, a function of transporting theelectrons, and a function of obstructing holes injected from the anode.Specific examples thereof include a triazole, a triazine, an oxazole, anoxadiazole, a fluorenone, an anthraquinodimethane, an anthrone, adiphenylquinone, a thiopyrane dioxide, a carbodiimide, afluorenilidenemethane, a distyrylpyrazine, a silole, an aromatic ringtetra-carboxylic acid anhydride such as naphthaleneperylene, aphthalocyanine, various kinds of metallic complexes, such as a metalliccomplex of a 8-quinolinol derivative and a metallic complex having metalphthalocyanine, benzoxazole, or benzothiazole as a ligand, andderivatives of the above-mentioned compounds.

Film thickness of the electron injecting layer and the electrontransporting layer are not particularly limited, and in general, arepreferably from 1 nm to 5 μm, more preferably from 5 nm to 1 μm, stillmore preferably from 10 nm to 500 nm.

The electron injecting layer and the electron transporting layer mayeach have a single layer structure of one or more kinds of theabove-mentioned materials or, alternatively, a multilayer structurecomprising plural layers having the same composition or differentcompositions.

A material for the light-emitting layer is not particularly limited aslong as it is capable of forming a layer in which it is possible forholes to be injected thereto from the anode, the hole injecting layer orthe hole transporting layer upon application of an electric field, andin which it is possible for electrons to be injected thereto from thecathode, an electron injecting layer or the electron transporting layer.The material for the light emitting layer must also function to transferthe injected charge and to provide a place for the recombination ofholes and electrons to emit light.

Examples of a compound to be used in the light emitting layer include: abenzoxazole, a benzimidazole, a benzothiazole, a styryl benzene, apolyphenyl, a diphenyl butadiene, a tetraphenylbutadiene, anaphthalimide, a coumaline, a perylene, a perynone, an oxadiazole, anardazine, a pyralizine, a cyclopentadiene, a bisstyrylanthracene, aquinacridone, a pyrolopyridine, a thiadiazolopyridine, a styrylamine,aromatic dimethylidine compounds, metal complexes of 8-quinolinolderivatives, metal complexes of phenylpyridine derivatives, varioustypes of metal complexes represented by organic metal complexes and rareearth metal complexes, polymer compounds such as polythiofene,polyphenylene and polyphenylenevinylene, and derivatives of theabove-mentioned compounds.

Here, at least one kind of the materials contained in the light emittinglayer is preferably provided as the above-mentioned phosphorescenceemitting material.

A film thickness of the light emitting layer is not particularlylimited, and is preferably from 1 nm to 5 μm, more preferably from 5 nmto 1 μm, and still more preferably from 10 nm to 500 nm.

A material for the protective layer may be those having a function ofsuppressing entrance of substances that accelerate deterioration of theelement, such as moisture and oxygen, into the element.

Specific examples thereof include metals, such as In, Sn, Pb, Au, Cu,Ag, Al, Ti and Ni, metallic oxides, such as MgO, SiO, SiO₂, Al₂O₃, GeO,NiO, CaO, BaO, Fe₂O₃, Y₂O₃ and TiO₂, metallic fluorides, such as MgF₂,LiF, AlF₃ and CaF₂, polyethylene, polypropylene, polymethylmethacrylate, polyimide, polyurea, polytetrafluoroethylene,polychlorotrifluoroethylene, polydichlorodifluoroethylene, a copolymerof chlorotrifluoroethylene and dichlorodifluoroethylene, a copolymerobtained by copolymerizing a monomer mixture containingtetrafluoroethylene and at least one kind of comonomer, afluorine-containing copolymer having a cyclic structure in a copolymermain chain, a water absorbing substance having a water absorption rateof 1% or more, and a moisture preventing substance having a waterabsorption rate of 0.1% or less.

A method of forming the protective layer is also not particularlylimited, and examples of applicable forming methods thereof include avacuum deposition method, a sputtering method, a reactive sputteringmethod, a molecular beam epitaxy (MBE) method, a cluster ion beammethod, an ion plating method, a plasma copolymerization method(high-frequency excitation ion plating process), a plasma CVD method, alaser CVD method, a heat CVD method, a gas source CVD method, a coatingmethod, an ink jet method, a printing method, a tranfer method, and anelectrophotographic method.

The materials of the anode may comprise a metal, an alloy, a metallicoxide, an electroconductive compound, or mixture thereof,

Examples of a material for the anode include metals, alloys, metallicoxides, electroconductive compounds and mixtures thereof, and a materialhaving a work function of 4 eV or more is preferable. Specific examplesthereof include electroconductive metallic oxides, such as tin oxide,zinc oxide, indium oxide and indium tin oxide (ITO), metals, such asgold, silver, chromium and nickel, mixtures or laminates of these metalsand electroconductive metallic oxides, inorganic electroconductivesubstances, such as copper iodide and copper sulfide, organicelectroconductive materials, such as polyaniline, polythiophen andpolypyrrole, and mixtures or laminates of these materials and ITO. Amongthese, electroconductive metallic oxide are preferable, and ITO isparticularly preferable from the standpoint of productivity, highelectroconductivity and transparency.

A film thickness of the anode can be appropriately selected depending onthe material, and in general, is preferably from 10 nm to 5 μm, morepreferably from 50 nm to 1 μm, and still more preferably from 100 nm to500 nm.

The anode is generally formed as a layer on a transparent substrate,such as soda lime glass, non-alkali glass or a transparent resinsubstrate. When glass is used as the transparent substrate, the glassmaterial is preferably non-alkali glass in order to reduce eluted ionsfrom the glass. When soda lime glass is used, it is preferable to use asoda lime glass having a barrier coating of, for example, silica. Athickness of the substrate is not particularly limited as long as itsufficiently maintains mechanical strength, and is generally 0.2 mm ormore, and preferably 0.7 mm or more when glass is used.

The anode can be produced by various methods depending on the material,and in the case of ITO, for example a film thereof may be produced by anelectron beam method, a sputtering method, a resistance heating vapordeposition method, a chemical reaction method (a sol-gel method), aspraying method, a dip coating method, a thermal CVD process, a plasmaCVD process, coating method in which a dispersion of indium tin oxide isapplied, or the like.

If the anode is subjected to various treatment, such as cleaning, adriving voltage of the light emitting element can be decreased, andlight emission efficiency thereof can be improved. In the case of ITO,for example, a UV-ozone treatment, a plasma treatment, and the like areeffective.

The cathode is for supplying electrons to the electron injecting layer,the electron transporting layer, the light emitting layer or the like,and is selected in consideration of adhesion to a layer adjacent to thecathode, such as the electron injecting layer, the electron transportinglayer or the light emitting layer, ionization potential and stability.

Examples of a material for the cathode include metals, alloys, metallicoxides, electroconductive compounds and mixtures thereof. Specificexamples thereof include alkali metals (such as Li, Na and K) andfluorides thereof, alkaline earth metals (such as Mg and Ca) andfluorides thereof, gold, silver, lead, aluminum, alloys or metallicmixtures of sodium and potassium, alloys or metallic mixtures of lithiumand aluminum, alloys or metallic mixtures of magnesium and silver, andrare earth metals, such as indium and ytterbium. Among these, a materialhaving a work function of 4 eV or less is preferable, and aluminum, analloy or a metallic mixture of lithium and aluminum, and an alloy or ametallic mixture of magnesium and silver are more preferable.

A film thickness of the cathode can be appropriately selected dependingon the material, and in general, is preferably from 10 nm to 5 μm, morepreferably from 50 nm to 1 μm, and still more further preferably from100 nm to 1 μm.

The cathode can be produced by various methods, such as an electron beammethod, a sputtering method, a resistance heating vapor depositionmethod and a coating method, and a metal may be vapor-deposited as asingle substance or, alternatively, two or more components may besimultaneously vapor-deposited. Furthermore, plural metals may besimultaneously vapor-deposited to form an alloy electrode, or an alloyprepared in advance may be vapor-deposited.

A sheet resistance of the anode and the cathode is preferably as low aspossible, and is preferably several hundred Ω per square or less.

The light-emitting element of the present invention can be applied totechnologies in various fields, such as display devices, displays,backlights, electrophotography, illumination light sources, recordinglight sources, exposure light sources, reading light sources, signs,signboards, interior lighting, optical communication and the like.

EXAMPLES

The present invention will be described in more detail below by means ofexamples. However, the invention is not intended to be limited by theseexamples.

Synthesis Example 1

Ltd.) was dissolved in 120 mL of tetrahydrofran, and this solution wascooled to −70° C. 18.6 mL of n-butyl lithium/n-hexane solution (1.6 M)(manufactured by Wako Pure Chemical Industries, Ltd.) was slowly drippedthereto for 30 minutes. After completion of the dripping process, theresulting solution was stirred at −70° C. for 30 minutes. 50 mL oftetrahydrofran solution containing 1.83 g of cyanuric chloride(manufactured by Tokyo Kasei Kogyo Co., Ltd.) was dripped thereto at−70° C., and the resulting solution was heated to room temperature, andstirred for 1 hour at room temperature. The reaction product was putinto water, and a deposited white solid matter was filtered out, andsufficiently washed with methanol and chloroform. After being dried, thestructure of the example compound (I-1) was confirmed by using amass-spectrum.

Example 1

Preparation of Organic EL Element

A glass substrate having dimensions of 25 mm×25 mm×0.7 mm, on which ITOwas coated at a thickness of 150 nm (manufactured by Sanyo VacuumIndustries Co., Ltd.), was used as a transparent supporting substrate.After etching and washing the glass substrate, TPD(N,N′-diphenyl-N,N′-di(m-tolyl)-benzidine) was vapor-deposited thereonto a thickness of 50 nm, the following compounds a and b werevapor-deposited (N,N′-diphenyl-N,N′-di(m-tolyl)-benzidine) wasvapor-deposited thereon to a thickness of 50 nm, the following compoundsa and b were vapor-deposited thereon at a mass ratio of 34:2 to athickness of 36 nm, and the exemplified compound (I-1) was furthervapor-deposited thereon at a thickness of 36 nm.

After providing a patterned mask (providing a light emission area of 4mm×5 mm) on the organic thin film, lithium fluoride was vapor-depositedto a thickness of 3 nm, and then aluminum was vapor-deposited to athickness of 60 nm, whereby an organic EL element of example 1 wasproduced.

Evaluation

Evaluation Method

The resulting organic EL element was subjected to light emission byapplying a constant direct current voltage by using a source measuringunit ‘Type 2400 produced by Toyo Corp.’ and the luminance was measuredby using a luminance meter ‘BM-8 produced by Topcon Corp’.

The light emission wavelength and the CIE chromaticity coordinate weremeasured by using spectrum analyzer ‘PMA-11 produced by HamamatsuPhotonics Co., Ltd.’.

Evaluation Results

As a result, light emission with CIE chromaticity coordinates of (x,y)=(0.19, 0.48) was obtained, and the external quantum efficiencythereof was 7.6% (light emission from an excited triplet state).

The same evaluation was carried out after the resulting element had beenleft at room temperature for a week, and the external quantum efficiencythereof was 7.4%.

Comparative Example 1

An organic EL element of comparative example 1 was produced in the samemanner as in example 1 except that a compound C shown below was usedinstead of the exemplified compound (I-1).

The resulting organic EL element was evaluated in the same manner as inexample 1. As a result, light emission with CIE chromaticity coordinatesof (x, y)=(0.24, 0.55) was obtained, and the external quantum efficiencythereof was 1.7%.

The same evaluation was carried out after the resulting element had beenleft at room temperature for a week, and the external quantum efficiencythereof was 0.4%.

Example 2

α-NPD (N,N′-diphenyl-N,N′-di(α-naphthyl)-benzidine) was vapor-depositedto a thickness of 40 nm on an ITO substrate washed in the same manner asin example 1, a compound d shown below (blue light emitting material)was vapor-deposited to a thickness of 20 nm, and the exemplifiedcompound (I-1) was vapor-deposited thereon to a thickness of 40 nm.

After providing a patterned mask (providing a light emission area of 4mm×5 mm) on the obtained organic thin film, magnesium and silver (10/1)were simultaneously vapor-deposited to a thickness of 50 nm, and thensilver was vapor-deposited to a thickness of 50 nm, whereby an organicEL element of example 2 was produced.

The resulting organic EL element was evaluated in the same manner as inexample 1. As a result, light emission with CIE chromaticity coordinatesof (x, y)=(0.15, 0.28) was obtained, and the external quantum efficiencythereof was 3.0% (light emission from an excitation singlet state).

The same evaluation was carried out after the resulting element had beenleft at room temperature for a week, and the external quantum efficiencythereof was 2.7%.

Comparative Example 2

An organic EL element of comparative example 2 was produced in the samemanner as in example 2 except that the above-mentioned compound C wasused instead of the exemplified compound (I-1).

The resulting organic EL element was evaluated in the same manner as inexample 1. As a result, light emission with CIE chromaticity coordinatesof (x, y)=(0.25, 0.47) was obtained, and the external quantum efficiencythereof was 1.8%.

The same evaluation was carried out after the resulting element had beenleft at room temperature for a week, and the external quantum efficiencythereof was 1.0%.

Example 3

Baytron P (manufactured by Bayer Corp.) was coated on an ITO substratewashed in the same manner as in example 1 by a spin coating method, andthen the substrate was vacuum-dried at 150° C. for 1.5 hours, whereby athin film having a film thickness of 70 nm was obtained. Then a solutionprepared by dissolving 40 mg of poly(N-vinyl carbazole) and 1 mg of theabove-mentioned compound b in 2.5 mL of dichloroethane was coatedthereon by a spin coating method to form a film having a film thicknessof 100 nm.

Further, the exemplified compound (I-1) was vapor deposited thereon to athickness of 40 nm. After providing a patterned mask (providing a lightemission area of 4 mm×5 mm) on the organic thin film, lithium fluoridewas vapor-deposited to a thickness of 3 nm, and then aluminum wasvapor-deposited to a thickness of 60 nm, whereby an organic EL elementof example 3 was produced.

The resulting organic EL element was evaluated in the same manner as inexample 1. As a result, light emission with CIE chromaticity coordinatesof (x, y)=(0.19, 0.50) was obtained, and the external quantum efficiencythereof was 1.5% (light emission from an excited triplet state).

The same evaluation was carried out after the resulting element had beenleft at room temperature for a week, and the external quantum efficiencythereof was 1.3%.

Comparative Example 3

An organic EL element of comparative example 3 was produced in the samemanner as in example 3 except that the above-mentioned compound C wasused instead of the exemplified compound (I-1).

The resulting organic EL element was evaluated in the same manner as inexample 1. As a result, light emission with CIE chromaticity coordinatesof (x, y)=(0.25, 0.53) was obtained, and the external quantum efficiencythereof was 0.2%.

The same evaluation was carried out after the resulting element had beenleft at room temperature for a week. However, no light emission wasobtained.

The results of examples 1 to 3 and comparative examples 1 to 3 show thatthe light emitting element of the present invention is superior in lightemitting characteristics (high luminance, high luminous efficiency, andhigh color purity), and has superior endurance.

In other words, in both of cases when light emission from an excitedtriplet state is utilized and cases when light emission from an excitedsinglet state is utilized, as well as even when a coating method thatnormally causes low luminous efficiency is used in preparing the lightemitting element, the light emitting element makes it possible toprovide high external quantum efficiency with superior light emittingcharacteristics and to also provide high endurance. The light emittingelement also improves the color purity in light emission colors.

As described above, in accordance with the light emitting element of thepresent invention, it becomes possible to provide a light emittingelement that has high luminance, high luminous efficiency, high colorpurity (in particular, purity of blue) and superior endurance.

1. A light emitting element comprising at least one organic layer whichincludes a light emitting layer, and which is disposed between a pair ofelectrodes, wherein at least one layer of the at least one organic layercontains at least one compound consisting of carbon, fluorine andnitrogen, wherein the compound is a compound represented by thefollowing general formula (A):X—(R)n   General formula (A) wherein in general formula (A), Xrepresents a hetero cyclic ring group selected from the group consistingof triazine, pyridine, pyrazine, quinoxaline and pyrrole; R represents agroup consisting of carbon and fluorine, or a group consisting ofcarbon, fluorine and nitrogen; and n represents an integer of 1 or more.2. The light emitting element of claim 1, wherein the compound hasaglass tranaition temperature in a range of 130° C. to 400° C.
 3. Thelight emitting element of claim 1, wherein light emission from anexcited triplet state is utilized.
 4. The light emitting element ofclaim 3, wherein when light emission from an excited triplet state isutilized, the compound has a minimum excitation triplet energy level of65 kcal/mol (272.2 kJ/mol) to 95 kcal/mol (68.05 kJ/mol).
 5. The lightemitting element of claim 1, wherein the compound is used as an electrontransporting material.
 6. The light emitting element of claim 5, whereinthe compound, which is used as an electron transporting material, iscontained in an amount of 60 to 100% by mass in an organic layercontaining theelectron transporting material.
 7. The light emittingelement of claim 1, wherein the compound is used as a host material in alayer containing a light emitting material.
 8. The light emittingelement of claim 7, wherein the compound, which is used as a hostmaterial, is contained in an amount of 50 to 99.9% by mass in an organiclayer containing the host material.
 9. The light emitting element ofclaim 1, wherein the at least one organic layer contains aphosphorescent material.
 10. The light emitting element of claim 9,wherein the phosphorescent material is a transition metal complex. 11.The light emitting element of claim 10, wherein the transition metalcomplex is selected from the group consisting of an iridium complex, aplatinum complex, a rhenium complex and a ruthenium complex.
 12. Thelight emitting element of claim 11, wherein the transition metal complexis an iridium complex.
 13. The light emitting element of claim 1,wherein the at least one organic layer is formed by a resistance heatingvapor deposition method, a coating method or a transferring method. 14.The light emitting element of claim 1, wherein the light emitting layeris formed by a coating method.